The invention represents an improvement over existing technology in use with burners, such as those described in U.S. Pat. No. 6,144,801, U.S. Pat. No. 6,451,841, U.S. Pat. No. 6,537,061, U.S. Pat. No. 6,814,929, U.S. 20050037309 and U.S. 20040265762. The aforementioned systems are composed of a burner, fuel, fuel reservoir, and a wick. The burners are composed of three main components: a porous ceramic body, a catalyst that is embedded in the porous ceramic body, and a wick that is inserted into the porous ceramic body.
The porous ceramic body is typically formed through the addition of a combustible material, such as carbon powder or sawdust, to a mixture of talc, clay, and binder to form a ceramic precursor. Once this mixture is extruded or molded into a desired shape the body is then calcined at >1000° C. to form the finished ceramic body. During the calcination process, the included combustible material is vaporized leaving voids, or pores in the ceramic body. Typical catalytic burners have an open porosity of 40%.
The catalyst is typically a stabilized alumina or silica microparticle supported precious metal catalyst such as those described in U.S. Pat. No. 4,029,602, U.S. Pat. No. 4,048,113, U.S. Pat. No. 4,301,035, and U.S. Pat. No. 4,368,029. The microparticle catalyst is mixed into liquid solution which is then applied to the surface of the porous ceramic body. The catalyst microparticles are smaller than the pores of the ceramic body, and are absorbed into the ceramic body and remain in place once the liquid is removed, in this manner the catalyst is embedded into the porous ceramic body.
The wick is typically composed of cotton or cellulose fiber, and is long enough so that it extends from the interior of the ceramic body to the bottom of the fuel reservoir. The fuel is typically composed of 90 wt % 2-propanol, 8 wt % H2O, and 2 wt % fragrance.
To operate the catalytic burners, the burner assembly is first placed on top of a fuel reservoir with the wick extending into the fuel/fragrance mixture. The fuel/fragrance mixture travels up the wick and into the pores of the porous ceramic body. Once the porous ceramic body is completely saturated, an open flame is applied to the surface of the ceramic body to ignite the absorbed fuel/fragrance mixture. The open flame is removed and the ignited fuel/fragrance mixture is allowed to burn. The burning fuel/fragrance mixture, which produces a ˜6 inch flame, is extinguished after ˜3 minutes. The igniting process serves two functions; first the flame consumes and/or desorbs the excess fuel from the porous ceramic body and second, once the excess fuel is desorbed, the flame heats the embedded catalyst particles to the appropriate temperature (˜150° C.) for continued operation. This starts a cyclical process in which the ceramic absorbs heat from the catalyst, the heated ceramic body vaporizes the fuel in the wick, the vaporized fuel passes over the catalyst and is combusted, and the catalytic combustion process provides heat back to the ceramic body. During this process the majority of the fuel/fragrance mixture is not consumed by the catalyst but is emitted into the surrounding atmosphere at a high rate, typically ˜12.0 grams/hour.
There are several problems, or drawbacks, associated with this system, such as: degradation of the cellulose wick, clogging of the pores in the ceramic body, large open flame (>6 inches) during start up, and long initial set-up (>15 minutes). Wick degradation occurs because, to achieve the necessary communication of the fuel with the catalytic burner, the wick must be in intimate contact with the catalytic burner, which can exceed temperatures of 250° C. during operation. The elevated temperature causes the cellulose wick to degrade and carbonize. Degradation of the wick causes the loss of fuel flow to the catalytic burner due to accumulation of the carbonized wick material in the pores of the ceramic burner and loss of intimate contact between the ceramic body and wick. The loss of fuel flow eventually causes irreversible failure of the catalytic burner. Clogging of the pores can also occur from accumulation of partially decomposed fragrance. During normal operation, a portion of the fragrance is not evaporated, but instead is decomposed inside the pores of the ceramic body. Over time, build up of this decomposed material occludes the pores of the ceramic and prevents the fuel vapor from reaching the catalyst.
The large flame that is necessary for start-up is a drawback of the system due to safety concerns. The large flame could easily ignite nearby drapes, paper, or other items, thereby causing uncontrolled fires. The currently available systems also require a long initial set-up (>15 min.) which is not consumer friendly. The catalytic burner assembly is placed in the pre-filled fuel reservoir and can not be operated until the fuel flows up the wick and completely saturates the catalytic burner, which can take longer than 15 minutes.
To overcome the above problems, a system has been developed in which the use of ceramic or other porous materials in the construction of burners is eliminated.